We have computed all the electronic states of ClO arising from the Cl(P-2) + O(P-3) dissociation limit and several of those connected with Cl(P-2) + O(D-1). Only two excited states have attractive potentials, A (2)Pi and 1 (4)Sigma(-). The A (2)Pi state undergoes a well known predissociation, because several as yet unknown potential curves cross the A (2)Pi one and are coupled to it by nonadiabatic and/or spin-orbit interactions. The calculation of the interaction matrix elements allows to explain the predissociation of A (2)Pi, due to transitions to the 3 (2)Pi, 1(2)Delta, 2 (4)Sigma(-) and other less important states, all leading to the Cl(P-2) + O(P-3) dissociation.